RFR: Cleanup allocation tracking in heuristics

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/heuristics-bytes-allocated/webrev.01/

This cleans up allocation tracking in heuristics. Most of the things are not used and bit-rotted
over the last year. The one thing that is still important to us -- bytes allocated since last cycle
-- is updated racily, and thus is unreliable.

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey